FIG. 2.

Kinetics of lung virus replication after primary (X31) or challenge infection with A/PR/8/34 influenza A virus in mice lacking receptors for IFN-α/β, IFN-γ, or both IFNs compared to their 129/SvEv congenic controls. Lung virus titers were measured following infection of naive (primary) IFNα/βR^−/−, IFNγR^−/−, IFNα/β-γR^−/−, or 129/SvEv control mice with 500 PFU of X31 (left panels) or following challenge of mice which had been primed with 500 PFU of X31 30 days previously with the heterologous A/PR/8/34 influenza (500 PFU i.n.) (right panels). Lung virus titers are expressed as the mean ± the standard error of the mean (SEM) log₁₀ TCID₅₀/gram of lung tissue of three to five mice.